Practically all radio frequency (RF) and antenna systems utilize a range of components such as phase shifters, power splitters, power combiners, RF hybrids, and baluns. In RF applications, these components are typically implemented as distributed functions either on gallium arsenide (GaAs) or other suitable RF substrate material. Though other materials may be used, GaAs is a higher quality material designed and controlled to provide good performance of electronic devices. However, in addition to being a higher quality material than other possible materials, GaAs is also more expensive and more difficult to manufacture. For phased array applications, these functions are typically implemented at every element in the phased array which greatly increases system size, weight, cost, and complexity.
Quadrature hybrids or other differential phase generating hybrids are used in a variety of RF applications. In an exemplary embodiment, quadrature hybrids are used for generating circular polarization signals, power combining, or power splitting. In an exemplary embodiment, the outputs of a quadrature hybrid have approximately equal amplitude and a 90° phase difference. In another typical embodiment, the quadrature hybrid is implemented as a distributed structure, such as a Lange coupler, or a branchline hybrid coupler. Other 180° hybrids, such as a magic tee or a ring hybrid, result in 180° phase shift. In general, quadrature hybrids and 180° hybrids are limited in frequency band and require significant physical space. Moreover, the quadrature hybrids and 180° hybrids are typically made of GaAs and have associated RF power loss on the order of 3-4 dB per hybrid when used as a power splitter, and an associated power loss of about 1 dB when used as a power combiner.
In particular, branchline hybrids are used for a variety of functions where generation or summation of quadrature signals is required. Applications include generation of polarization signals, power combining, power splitting, balanced amplifiers, and the like. Due to its distributed nature, the branchline hybrid is only capable of operating over a relatively narrow band of frequencies (typically 10% bandwidth) and requires significant physical space to be produced, particularly at lower frequencies where wavelengths are longer, such as C-band or below. Furthermore, a branchline hybrid typically results in significant RF ohmic losses.
In addition, ring hybrids are used for various applications, including generation of polarization signals, power combining, power splitting, and the like. Like the branchline coupler, due to its distributed nature, the ring hybrid is only capable of operating over a relatively narrow band of frequencies (typically 10% bandwidth) and requires significant physical space to be produced, particularly at lower frequencies where wavelengths are longer, such as C-band or below. Also, a ring hybrid typically results in significant RF ohmic losses.
Similarly, magic tee hybrids are used for various functions involving generation or summation of in-phase signals or 180° out-of-phase signals. Applications include generation of polarization signals, power combining, power splitting, and the like. One such typical application is using the magic tee hybrid in a waveguide. Due to its distributed waveguide nature, the magic tee hybrid is only capable of operating over a relatively narrow band of frequencies (typically 40% bandwidth) and requires significant physical space to be realized, making it impractical to use at lower frequencies.
Thus, a need exists for a fully integrated monolithic solution of a hybrid to replace a branchline hybrid, a 180° hybrid, a ring hybrid, or a magic tee while providing the same or similar functionality. Furthermore, a need exists for a hybrid that is compact and cost effective. Also, a need exists for a hybrid that has a wide operational bandwidth and does not suffer from high RF losses.